The point behind Pinkie's character seems to be that she loves just being alive, she just does things spontaniously because life can be so short, so she wants to make the most of her time while she has it; to stop and think about what she's planning on doing would waste valuable time in doing stuff

Andrew WK even comments on how Pinkie embraces the Party Hard attitude, just having fun and living life to the full; pretty much sums it up, really